Measurement of pressure differentials



Aug. 2, 1932. c. A. uNDERwooD 1,369,400

MEASUREMENT OF PRESSURE DIFFERENTIALS Filed June 12. 1'930 i' s Sheets-'sheet 1 F1- gj.

Z6 I v /5 L ji Z? INVENTOR C/qrence Wder/x/ao/ Aug 2, 1932- c. A. UNDERwooD 1,86954'00 MEASUREMENT OF PRESSURE DIFFERENTIALS Filed June 12. 1950 3 Sheets-Sheet 2 INVENTOR C/arefzc'e Underwood f ATTORNEYS AUS- 2, 1932A c. A. uNDERwooD 1,869,400

MEASUREMENT 0F PRESSUE DIFFERENTIALS Filed June l2. 1950 3 sheets-Sheet 3 zy@ T INVENTOR (/are//c f7. #ndern/aga' ATTORNEYS Patented Aug. 2, i932 UNITED Dsflua'ras CLARENCE A. UNDER'WOODJ,

or msm cnrcaeo, :NDIANA i MEASUREMENT QF'PRESSURE DIFFERENTIALS Application led J'une 12 This invention relates to improvements in instruments for measurino` differentials, in fiuid pressures, particularly as applied for indication of liquid levels and rates of fluid 5 How.

' Modern steam power plant practice has developed a necessity for remote water level indicators of extreme dependability and accuracy; increasing operating pressures and in- LO creasing evaporation rates have made water levels more critical and at the same time the height of boiler settings 'above firing floor levels has been' increasing. This invention provides 'particularly a remote water level .5 indicator of unusual simplicity meeting the requirements of such service.

The improvements of the invention are, however, of broader application; they are useful in connection with the indicationL of l liquid levels generall and Iin connection with the indication o rates of iow gener-y ally, of steam flow through.A a pipe for eX- ample.

The improved instrument of this invention l consists essentially bf a gauge glass and a pair of closed wells containing mercury connected below the normal mercury level, the upper end of the gauge glass being connected toA the upper part of one of the closed wells, a direct connection between the upper part of the other of the closed wells and the lower pressure region and a direct connection between the lower end of the gauge lass and the higher pressure region, means or maintaining both of these direct connections full of liquid, and a volumeof liquid, immiscible with the mercury and with the first men`v tioned liquid and visually distinct from the rst mentioned liquid, filling the connection between the upper end of the gauge glass'and the connected well, the upper'part of that well above the mercury andthe upper lend n of the gauge glass and normally establishing a meniscus in the gauge glass.

As applied for indication of boiler water level, the lower end of the gauge glass is connected directly to the boiler at a point below the normal boiler water level and the upper part of the second closed well is connected directly to the boiler at a. point above the nor- 1930. seria; No. $0,654.

mal boiler water level through a condenserarranged at the high point'of the connection and proportioned to maintain this connection full of water by condensation of steam irrespective of displacements due to variationsy in water level.-

As applied for indication of rates of Huid iow, steam ow for example an orifice is inserted in the pipe throu hwhich How is to 4be measured, the lower en of the gauge class is connected directly to this pipe'on the high pressure side of the orice through a condenser proportioned to maintain this connection full of water, and the upper part of `the second closed well is connected directly to this pipe through a condenser proportioned to maintain this connection full of water.

The invention will be described in moredetail in 'connection with the accompanying dra-wings which illustrate one form of water level indicator and one form of, ii'uid fiow indicator embodying the invention. It is intended and will be understood that this more detailed description and illustration are for the purpose of exemplication.

In the' accompanying drawings: l Fig. 1 is an elevation partly in section and with parts broken away of a water level indicator embodying the invention Aas connectedto a. boiler, Fig. 2 is an elevation with parts broken away of a fluid iow indicator embodying the invention as connected to a pipe the How through whichis to be measure Fig. 3 is a side elevation of the instrument illustrated in Fig. 2, and Fig. 4 is a plan of the instrument illustr ed in Fig. 2. p p f Fig. 5 is an elevation cfa water level indicator embodying the invention and connected to a boiler similar to that illustrated in Fig- ,ure 1 except that the larrangement provides for installation of the instrument at a `.point Aabocilve that at whichthe pressure isto-be measure Referring to Fig. 1,'the boiler water level indicator illustratedcomprises a gauge glass 5, a pair 'of closed'wells 6 and 7 connected by` a passage 8 including a drain plug 9, a con- `nectio'n 1() including a movable plug 11 between the upper part of the well 6 and the upper end of the gauge glass 5, a direct connection 12 including a drain plug 22 and removable plugs 13 and 16 between the lower end of the gauge glass 5 and the boiler 14, at a point below the normal boiler water level, and a direct connection 15 including removable plugs 17 and 18 and a` condenser 19 between the upper part of the well 7 and the boiler 14, at a point above the normal boiler water level. The connections may, as illustrated, be connected directly to the lower and upper parts respectively of the usual gauge column 20. The usual gauge column blowdoWn linefis indicated at 21.

With the instrument arranged as illustrated in Fig; 1, it is put in operation as follows: lVith the lvalves 26 and 27 closed, the drain plugs 9 and 22 are,` fitted tightly in place and the plugs 17, 11, and 13 are removed. The wells 6 and 7 are half-filled (as indicated in the drawings) with mercury through plug 11. .lVater is poured through plug 13 until. a water level just shows in the lower end of the gauge glass 5 and the valve 23 is then closed. A liquid immiscible with mercury and with water and visually distinct from water isv poured through plug 11 until it overflows andv the plug 11 is then fittedtightly in place.

Water is poured through plugs 17 and 13 until it overflows, at levels fixed by the levels of the upper faces of the fittings 24 and 25 respectively, and the plugs 17 and 13 are then fitted tightly in place. With the'valves 26 and 27 still closed, water is poured .through plugs '18 and 16 until it overflows and these plugs are then fitted tightlyinplace. Valve,

23 is then opened and the water level :in the gauge glass 5 is again brought to a point such that it is just visible in the lower end of the gauge glass by permitting, if necessary, a slow escape of sufficient liquid from connection 10 through the plug 11. The plug 11 having been fitted tightly in place again, the valves 26 and 27 are thereupon opened and the meniscus in the gauge glass 5 immediately assumes a position' corresponding to the meniscus in the gauge glass 28 of the usual gauge column 20. Once placed in operation,

the condenser'19 maintains theconnection 15 ful-l of water thus maintainingA a constantv head over the mercury in the well 7 against which fhxctuations in water level ,are balanced through the connection 12 by displacement of the mercury with corresponding displacement of the meniscus in the gauge glass-5.

The wells 6 and 7 are carefully machined inside to have the same area of internal horizontal section throughout. By proportioning the area of this section to the area of the internal horizontal section of the gaugeglass 5, variation in water level in the boiler may be indicated by an identical variation in level of the meniscus in thegauge glass 5 or by a When so arranged, the instrument may be put i,

in operation with a minimum of difficulty, as just described, by bringing it to a normal equilibrium against the extreme levels fixed by the position of these fittings.

For use in water level indicators embodying the invention', as just described, or in other applications of the invention involving contact with water, the liquid establishing the meniscus in the gauge glass 5 may consist of a mixture of equal parts of kerosene and light lubricating oil colored, if necessary', by the addition of very small amounts of anilin. In such applications and in other applications of the invention the choice. of a liquid immiscible with mercury and with the liquid filling the connections to the instrument and visually distinct from the latter is determined by the chemical and physical properties of the latter liquid.

Referring to Figs. 2, 3 and 4, the steam flow indicator illustrated comprises a gauge glass 29, a. pair of closed wells 30 and 31 connected by a passage 32 including a needle valve 33, a connection 34 including a removable plug 35 between the upper part of the lwell 30'and the upper end of the gauge glass 29, a connection 3,6 including a drain plug 37 and a condenser 38 between they lower end of the gauge glass 29 and the high pressure side of the orifice 39 in the steam line 40, and a connection 41 including a condenser 42 between the upper part of the well 31 and the low pressure side of the orifice 39 in the steam line 40. A by-pass connection 43 between the connections 41 and 36 is, provided to facilitate adjustment of the instrument. Needle valves 56 and 57 are advantageously provided in connections 36 and 41, respectively.

With the instrument arranged as illustrated in Figs. 2, 3 and 4, it is put vin operation as follows With the plugs 44 and 45 out,

with the needle valve 33 open, or partly open, with the by-pass 43 closed and with the valves 46 and 47 closed, the wells 31 and 30 are halffilled with mercury through the plug 35. Water is then' poured through the plug 45 until a water level just shows in the lower end of the gauge glass 29. The valve 48 is then closed. A liquid immiscible with mercury and with water and visually distinct from water is then poured through the plug 35 until it overflows and the plug 35 is fitted tightly in place. Water is then poured through the plug 44 until it overflows and the through the plug 35 again to make the waterl ICI level in the gauge glass 29 just visible at the lower end. The Valves 46 and 47 are then opened in this order, valve 47 being opened slowly. The needle valve 33 is adjusted to eliminate surging or oscillation within the instrument. i

The indication in the gauge glass 29 of the pressure differential across the orifice 39 is an indication of rate of fiow through the orifice. The scale 49 may be calibrated to meet any particular requirement. By. properly proportioning the ratio of the area of the internal horizontal section of the wells 31 and and the area of the internal horizontal section of the gauge glass 29, the relative displacement of 'the meniscus in the gauge glass 29 may be magnied or diminished as desired.f"In this way, low rates of flow may be measured accurately withlarge orifices,

eliminating the introduction of large losses through resistance to flow throu h the orifice, since the instrument will magni y the Jsmaller pressure differentials resulting from the use of larger orifices.

The improved instrument of the invention can be installed at convenient distances from the point in any system to which it is connected. It may also be installed above or below the level of such a point of connection". If installed above, the connections between the instrument and the system should include suitable traps or seals.

With the instrument arranged asillusu trated in Fig. 5; it is putin operation exactly as described in connection with4 the instrument illustrated in Fig. 1 except `that the valves 52a and 53a should be initially closed and remain closed until all of the connections have been filled and the instrument is ready to be placed in actual operation. The instrument illustrated in Fig. 5 is substantially identical with Fig. 1eXcept that the correspondin parts have been identified by the same re erence numerals with the letter a appended thereto. The instrument illustrated in Fig. 5 differs from Ithe instrument illustrated in Fig. 1 only in'that connections a and 51a are extended upwardly to raise the instrument to any desired height. In this arrangement the lower portion of con'- nections 50a'and 51a together with connections 54a and 55a form suitable traps onn seals which serve to preventfescape of liquid from the connections. V

The means provided in the lustrated in the accompanying drawings for .maintaining the connections between the instrument and the system to which it is connected full of liquid consist of a condenser or condensers providing liquid by condensa-l tion of vapor derived from the system, by the condensation of steam inthe applications illustrated. As applied to systems not containing condensible vapor, indication of the .rate ofliow of a non-condensible gas through instruments ilthe pipe 40 in the apparatus illustrated in' Figs. 2, 3 and 4 or indication of a water level in a cold tank or reservoir withapparatus similar to that illust-rated in Fig. l for` eX` ample, a liquid' may be supplied to either'\or both of the connections between the instru,-

ment and the system, as may-be necessary, at' l a rate sufficient to maintain these connections full of liquid, for example, from a source -of a liquid under higher pressure through needle valves 56 and 5,7 opening into the re spective connections. As applied to indication of the rate of fiow of a liquid with liquid through pipes, of vthe through filters, and so forth.

I claim: 1. An instrument foimeasuring pressure differentials comprising a gauge glass, a pair pressure `drop 'and reservoirs, of the rate of flow of' gas or of closed yWells containing'mercury and con- -1 nected below the normal mercury level, a connection between the upper end of the gauge class and the upper part 'of one of the closed wells; a direct connection between the upper part of the other of the closed lwells and the lower pressure region, a direct connectionfbetween the lower end of the gauge glass and the'hiv her pressure reglon, means for maintaining oth ofI these direct connections full of liquid, and a volume of liquid,

immiscible with the mercury andv with the first-mentioned liquid and visually distinct from the first-mentioned liquid, filling the connection between the upper end of the gauge glass andthe connected well, the upper part of that well above the mercury and the upper end of the gauge glass and norass.

2. In combination-with -a boiler, the instrument defined in claim 1, the connection from `the lower end of the gauge glass being arranged to communicate directly with a point in the boiler below the normal water level therein, and the connection between the upper part'pf tliemercury well leading directly tothe regionof lower pressure and being connected to the boiler at a point above the normal water level therein, said last mentioned connection including a condenser.

3. In combination with an orifice in a pipe the rate of ow through which is to be meas ured, the instrument defined in claim 1,the connection from the lower end of the gauge glass being arranged to communicate direct` ly with a point in the pipe on the upstream `nally Vestablishing a meniscus in the gauge g side of the orce and the connection between the upper part of the mercury Well leading directly to the region of lower pressure being arranged to communicate directly with 4a. point n the pipe on the downstream side n of the orce.

In testimony whereof Lafx my signature.

CLARENCE A. UNDERWOOD. 

